Initial snapshot: hand motion pipeline (Dyn-HaMR + dex-retargeting + SPIDER)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

model/__init__.py

@@ -0,0 +1,30 @@
+"""HandFlow model package — attention function with flash-attn fallback."""
+
+import torch
+from einops import rearrange
+from torch import Tensor
+
+FA3_FOUND = True
+try:
+    from flash_attn_interface import flash_attn_func  # noqa: F401
+except ImportError:
+    FA3_FOUND = False
+
+if FA3_FOUND:
+
+    def attention(q: Tensor, k: Tensor, v: Tensor) -> Tensor:
+        q = rearrange(q, "B H L D -> B L H D")
+        k = rearrange(k, "B H L D -> B L H D")
+        v = rearrange(v, "B H L D -> B L H D")
+        x = flash_attn_func(q, k, v)
+        if not isinstance(x, Tensor):
+            x = x[0]
+        x = rearrange(x, "B L H D -> B L (H D)")
+        return x
+
+else:
+
+    def attention(q: Tensor, k: Tensor, v: Tensor) -> Tensor:
+        x = torch.nn.functional.scaled_dot_product_attention(q, k, v)
+        x = rearrange(x, "B H L D -> B L (H D)")
+        return x